Taurine deficiency in the cat is associated initially with photoreceptor cell malfunction and then with photoreceptor cell death. The proposed biochemical studies may help to explain the mechanism(s) whereby taurine deficiency initially alters photoreceptor cell function. The process(es) by which taurine concentrations are maintained in the retina is not known. The relative importance of in situ synthesis of taurine in the retina or the dependence of retinal taurine on plasma taurine levels will be considered in these experiments. Uptake and metabolism of S35 labelled taurine in the retina will be studied in normal and taurine deficient cats to determine the possible function of taurine in light or dark adaptation. These studies should lead to a better understanding of the biological role of taurine in maintaining photoreceptor cell function and viability.